Multiple recording instrument



July 8, 1947. J. A. CALDWELL MULTIPLE RECORDING INSTRUMENT Filed June20, 1942 10 Sheets-Sheet 1 FIG.

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JOHN A. CALDWELL LINE ATTORNEY.

y 1947- J. A. CALDWELL 2,423,480

MULTIPLE RECORDING INSTRUMENT Filed June 20, 1942 10 Sheets-Sheet 2INVENTOR. JOHN A. CALDWELL ATTORNEY.

FIG. 2.

y 1947- J. A. CALDWELL MULTIPLE RECORDING INSTRUMENT Filed June 20, 194210' Sheets-Sheet s INVENTOR. JOHN A. CALDWELL BY 5 M ATTORNEY.

July 8, 1947- J. A. CALDWELL MULTIPLE RECORDING INSTRUMENT Filed June20, 1942 1O Sheets-Sheet 4 ill llFllP 3 --7l pp.

INVENTOR. JOHN A. CALDWELL BY W TORNEY.

y 1947- J. A. CALDWELL 2,423,480

MULTIPLE RECORDING INSTRUMENT Filed June 20, 1942 1,0 Sheets-Sheet 5INVENT OR. JOHN A. CALDWELL BY Q TORNEY.

y 1947- J. A. CALDWELL 2,423,480

I MULTIPLE RECORDING INSTRUMENT Filed June 20, 1942 10 Sheets-Sheet 6INVENTOR. JOHN A. CALDWELL FIG. l4.

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July 8, 1947.

J. A. CALDWELL MULTIPLE RECORDING INSTRUMENT 10 Sheets-Sheet 7 FiledJune v20, 1942 FIG. [2A.

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10 Sheets-Sheet 8 J. A. CALDWELL MULTIPLE RECORDING INSTRUMENT F iledJune 20, 1942 w w. wvwgllllkt i l j n 4 a 4 d v I a I v I 1 I 1 I 1 v iL U 4 July 8, 1947.

INVENTOR. JOHN A. CALDWELL lwm HWM IH F L U T s j L H IUHHHHHIFFMLTORNEY.

INVENTOR.

mama! .1. A. CALDWELL MULTIPLE RECORDING INSTRUMENT Filed June 20, 1942July 8, 1947.

JOHN A. CALDWELL BY 5% FIG. 24.

MULTIPLE RECORDING INSTRUMENT Fi led June 20, 1942 10 Sheets-Sheet 10 il l 'n m y ""1 IN V EN TOR- (355 354 39 JOHN A. CALDWELL ATTORNEY.

Patented July 8, 1947 UNITED STATES PATENT. OFFICE MULTIPLE RECORDINGINSTRUMENT John. A. Caldwell; Philadelphia, Pa, assignor to TheBrownlnstrument Company; Philadelphia, Pa., a corporation ofPennsylvania Application June 20,1942, Serial No. 447,863

exhibiting element, and in somecases to operate a control. Each oftheseinstruments must in herently move the exhibiting element in a series ofsteps until it is properly positioned. Thereafter, it the instrument isa multiple recorder, som means is used tomove the-marking element intoengagement withv the chart and" to subsequently connect the instrumentto another con dition, tobe measured and recorded.

With few exceptions, a multiple IGCOI'diIlg instrument is made tomeasure and record each condition within given periods of time.

together a recording operation can not occur until after the given,-period of time ha expired, even though the instrument almost immediatelypositions the marker. In another type of recording, instrument, arecord. of the value of the condi tionis made apredetermined number ofcycles after the marker is properly positioned. Both types of.instruments require an excessive period of. time after the marker isproperly positioned;

before the recording operation cantake place.

It is an, object of myinvention to provide a; multiple potentiometerinstrument which is not cyclic in operation so that the marker may becontinuously and rapidly moved to recording position. It is" a. furtherobject of the invention, to provide means to make the record of thevalueof the, condition substantially immediately after Ifthe conditions beingmeasured have their values close immediately after the instrumentreaches a balanced condition to actuate the printing mechanism. This.detecting mechanism is quiet in operation as well as being positive inthe performanceof its functions. g

It is a further object of the invention toprovide a recording instrumentin which the. chart is easily accessible for inspection and may bereadily and quickly changed when anew. chart is needed. The chart supplyand rewind mechanism is also. supplied with novel adjusting means tocompensate for irregularly wound'rolls or chart paper.

It is a further object of the invention to provide a multiplepotentiometer havin only two contin uously driven parts. These. partsare. the above mentioned detecting and chart drivin mechanisms. Theother movi g. parts of the instrument operate only when a conditionchange is. occurring and when a record is made of the same. It is afurther object of the invention, toprovide a. multiple potentiometerinstrument in, which the various parts are so positioned relative toeach other that a. compact, readily accessible instrument is provided.The parts are so placed that adjustments and repairs, when, necessary,may be made easily and in a minimum of time. The arrangement is suchthat the casing is no larger than that used for the ordinarypotentiometer.

'The various features of novelty which. characterize my invention arepointed out with. particularity in the claims annexed to and formin apart of thi specification. For a better understanding of the invention,however, its. advantages and. specific objects obtained with its. use,

reference should be had to the accompanying drawings and. descriptive.matter in which I have illustrated and described a preferred embodimentof the invention.

In the drawings-.-..

Figure; l is a schematic; diagram of the potentiometer circuit andinstrument,

Figure 2. is. a. front View of the instrument in it casing with certainportionsbroken away;

Figure 3 isa top view. of the instrumenttaken on line 3--3 of Figure 2,

Figure 4 i a detail of the slide-wire adjusting means,

Figure 5 is a section taken on line 5-5 of Figure 4,

Figure 5A is a view of a portion of the frame looking from, the right inFigure 3,

Figure 6 is a front view of the instrument casing with the recordinmechanism. removed,

Figure 7 is a view, partly in section, of the cold junction compensatingresistor,

Figure 8 is a back view of the supporting frame for the recordingmechanism, with certain portions broken away,

Figure 9 is a section taken on line 9-9 of Figure 8,

Figure 16 is a sectional view showing a chuck for supporting one end ofboth the chart supply roll and chart take-up roll,

Figure 11 is a sectional View showing a supporting chuck for the otherend of the supply roll,

Figure 12 is an outside view of the left-hand side of the frame of theinstrument with associated parts mounted thereon,

Figure 12A is a section view of a pulley moun E.

Figure 13 is an enlarged view of a driving pawl,

Figure 14 is a view taken from the top of Figure 13,

Figure 15 is a view of a modified form of detector cam,

Figure 16 is a view of another modified form of detecting cam,

Figure 17 is a view of a portion of the inside of the left-hand side ofthe instrument frame.

Figure 18 is an inverted view taken on line I8l8 of Figure 12 and adirect view taken on line l8l8 of Figure 17,

Figure 19 is a side view of the print wheel carriage looking from theright in Figure 2,

Figure 20 is a sectional view of a portion of the print wheel carriage,

Figure 21 is a view taken on line 2l--2l of Figure 19,

Figure 22 is a view taken on line 2222 of Figure 21,

Figure 23 is a view taken on line 23-23 of Figure 19,

Figure 24 is a side view of a modified form of chart drive mechanism,

Figure 25 is a view taken on line 25-25 on Figure 24,

Figure 26 is a view of a modified form of a slidewire assembly,

Figure 27 is a bottom view of the Figure 26,

Figure 28 is a view taken on line 28-28 of Figure 26,

Figure 29 is a view taken on line 29-29 on Figure 26,

Figure 30 is a view taken on line 30-40 on Figure 26,

Figure 31 is a view of a modified form of drive crank, and

Figure 32 is a view looking from the right at Figure 31.

Referring first to Figure 1, there is shown schematically a wiringdiagram of a potentiometer of the self-balancing type which may be usedto indicate, record, and/or control the value of a condition beingmeasured. For purposes of this description it may be assumed that theconditions being measured are temperatures. For this purpose there areshown four thermocouples T, although any other desired number may beused.

The thermocouple T which is responsive to the temperature that is to bemeasured, operates in conjunction with a potentiometer network which isgenerally designated at l to form a self-balancing potentiometer system.Upon a change in temperature to which the thermocouple is subjected anunbalanced D. C. current in one direction or the opposite is produceddepending upon the direction of unbalance of the potentiometer system.This D. C. current is supplied to an amplifier unit 2 having a vibratoror equivalent device designated at 3 and a transformer designated at 4which are connected to an amplifying circuit that is not shown. Thevibrator 3 preferably is of the form disclosed and claimed in theco-pending application of Frederick W. Side, bearing Serial Number421,176.

The direct current supplied to the amplifier is converted by thevibrator to a pulsating current of one phase or of an opposite phasedepending upon the sense of unbalance of the potentiometer system. Thispulsating current is detected by the transformer 4 and is amplified by avacuum tube system which may take the form of that shown in thecopending application of Walter P. Wills filed December 1, 1941, andhaving Serial No. 421,173. The current from the amplifier is used foroperating a reversible motor generally designated at 5 in one directionor the opposite direction. This motor serves to operate a slide wireassembly to rebalanoe the potentiometer system and also serves to movean indicating and recording mechanism which will be described in detailbelow.

The potentiometer network may comprise three resistances, 6, 1, and 8which are connected in series. These resistances are usually formed ofsome wire having substantially no temperattue resistance coeflicient andmay be used for calibration purposes. Connected in parallel to theseresistances are a battery 9 which may be in the form of a dry cell and adual vernier rheostat comprising resistances l0 and II and electricallyconnected sliding contacts 12 and I3 which engage with the resistancesI0 and II respectively. The rheostat may be operated by any suitabletype of knob, there being a direct mechanical connection between theknob and the contact l2 and a lost motion connection between the knoband the contact I 3. Upon initial movement of the knob, the contact I2is first moved and then the contact [3 is moved thereby providing avernier adjustment. The battery 9 and the rheostat are connected inseries with respect to each other and in parallel with the resistances6, T, and 8. Also connected in parallel with the first mentionedresistances are two other resistances l4 and I5, which are in turnconnected in series with each other. The resistance M is preferably madeof copper or other material having a suitable tcmperature resistancecoeflicient and the resistance I 5 may be made of manganin havingsubstantially no temperature coeflicient of resistance. The resistance 14 operates to compensate for temperature changes at the cold junction ofthe thermocouple and is so connected into the network that the voltagedrop across it is added to the thermocouple E. M. F. The resistance I5is utilized primarily for standardization purposes and has a resistancevalue such that the voltage drop across it is equal to the voltageproduced by the standard cell.

The slidewire assembly consists preferably of a coil l6 which is woundaround and insulated from a core 11. Cooperating with the slide wire isa collector'bar l3 which is also wrapped around a core l9. The slidewire and the collector bar are electrically connected by a slidingcontact 20 that is driven by the motor 5 to rebalance the potentiometercircuit. The terminals of the slide wire I6 and its core I! areconnected in parallel around the resistance 7.

A two position switch 2| is connected into thev potentiometer networkand serves the purpose of performing two functions; namely, for:c'onnecting the potentiometer .circuit for normal operation (run) andforstandardizing the potentiometer system (standardizing).:Schematically, this switchmay comprise a plurality of. switch armsofwhich arms 22 and '23 "are moved together by means 'ofaknob 24.'Switcharm'22 carries on it a contact 25 and the switch '23 carrieson'it a contact 26,'which contacts are adapted to engage respectivelycontacts 21 and 28 that are carried by otherarmsin'the switch assembly.The contact 28 is-connected with one lead from one of the thermocouplesT. This lead is shown as including a'wire '29 which terminates in a coldlunction 38 that is located closely adjacent toiresistance I4. Connectedto the junction 30 is a 'resistance 3I which hasa condenser 32inparallel with it and a wire 33 that leads to the switch con tact 28. Theother thermocouple lead runs directly through wire 34 to a second coldjunction 35, which is also located adjacent resistor I4 -and from therethrough a wire '36 to the collector core IS.

The switch 2I i shown in the run position. When the switch is in itsstandardizingposition the contact 25 engages a contact 31 andthe-contact 26 engagesacontact 38.

schematically shown as forming a portion of the amplifier 2 is thetransformer 4. This transformer comprises a primary winding 39 which hasa center tap 39'. Primary winding .39 is wound around a core structure4I that also has on it a secondary winding 42 that isconnected with theamplifier. A shield is provided between the primary and secondarywindings and all of these parts may be cased in a suitablehousing.

Also shown in a schematic manner is vibrato-r 3 which comprises avibrating reed 43 that normally engages contact 44 and 45 but whichduring its vibration will separate first from contact 44 and then fromcontact 45. The reed is vibrated under the influence of a Winding 46that is connected to a suitable source of alternating current. Apermanent magnet 41 is associated with the reed and is used forpolarization and synchronizing. This structure is also enclosedin asuitable housing. One end of the primary winding 39 of the transformeris connected by a wire to the contact 45 of the vibrator, while theother end of the primar winding is connected by a wire 50 to the contact44. The center tap 39' of the primary winding is connected by means of aWire 48 with the contacts 25 and 26 so that it can b connected into thepotentiometer circuit. Vibrating reed 43 is connected by means of Wires48 and 49 with the potentiometer circuit between resistances I4 and I5.The effect is that a circuit is completed through the thermocouple, thevibrator and the transformer to the potentiometer circuit, and ineffect, the vibrator and transformer serve substantially the samefunction as a galvanometer in an ordinary potentiometer circuit.

From time to tim it becomes necessary to standardize the potentiometerand readjust the contacts I 2 and I3 to compensate for the decrease ofthe voltage of battery 9. To this end a standard cell 52 is connectedinto the potentiometer circuit by means of a wire 53 that connects thiscell with contact 31. When the switch '24 is in its lower orstandardizing position, the standard cell is connected through thetransformer and vibrator by means of the wires 48', 48, and 49 so that"it is placed in parallel around resistance I5. The same movement of theswitch'24 brings contacts 26 and 38 intoengagement to connect conductors48 and 54. This places a resistance 55 in shunt around the vibrator andtransformer.

.In the operation of the potentiometer system the battery 9 places apotential drop across the slide wire I6 a portion of which, dependingupon the position of contact 20, is opposed by the thermocouple voltage.When the potentiometer is in balance no current is flowing through thethermocouple circuit, but if the temperature which is being measured bythe thermocouple then connected in circuit changes, the thermocouplevoltage will change and current will flow in one direction or the otherthrough the potentiometer circuit to set up an alternating potential inthe secondary winding 42 which is in phase or out of phase with thealternatingsupply voltage. This alternating potential is amplified andused to control the operation of the motor 5 in the proper direction tomove contact 28 to rebalance the potentiometer circuit. If, for example,the temperature should increase, the thermocouple T then in circuitwould produce an increased E. M. F. and cause a current flow through thepotentiometer circuit. This current flow will go through wire 29, coldjunction 30, resistance 3|, wire 33, contacts 28, 26, and wire 48 to thecenter tap 39 of the transformer winding 39. From here the current willflow either through the upper or the lower half of this winding,depending whether the contact 45 or 44 is then engaging the reed 43 andthrough Wires 48 and 49 to the potentiometer circuit. This produces analternating potential in the transformer secondary 42 of one phase withrespect to the supply that is amplified by the amplifier to control theoperation of the motor 5 in the proper direction to rebalance thepotentiometer circuit. If the temperature had decreased, current wouldflow in the opposite direction or through wires 49 and 48 to thevibrator 3 and from the transformer through wire 46 creating analternating potential in the transformer winding 42 of the oppositephase with respect to the supply which is amplified to control theoperation of the motor 5 in the opposite direction. It will be noticedthat the motor 5, as illustrated, is a rotating field motor that has asquirrel cage rotor with interconnecting bars. Two of the oppositefields of the motor, the power windings, are connected across the supplylines 62 with a condenser 56 in one of the leads. The other oppositefields of the motor, the control windings, are connected to the outputof the amplifier 2, and have a condenser '51 in parallel with them. Eachpair of the motor field is connected in series. When the voltage andcurrent through the motor control windings lag the voltage and currentin thepower windings the motor will rotate in one direction. When thevoltage and current in the control windings lead those in the powerwindings, the motor will rotate in the opposite direction. The-amplifiershifts the phase of the current of the motor control winding so that themotor will rotate in the proper direction. As the motor rotates itdrives a pinion 258 integral therewith that engages a gear 58.

Attached to. movable with the gear 58 is a pulley 59 around which iswrapped an endless cable 653 connected. to contact 2! so that as themotor rotates, the contact will be moved in one direction or the otherto rebalance the potentiometer circuit in a manner above described. Oneend of the cable 68 runs over a pulley 45 that is carried by an arm I58pivotally mounted at I51 and biased by a spring I52 to take up the slackin the cable. The other end of the cable runs around a pulley 148 whichhas frictionally attached to it a detector member This detector memberis used in conjunction with other parts to be later described to detectbalance of the potentiometer or non-movement of the cable, to actuatethe marking mechanism that records the value of the temperature beingmeasured and to simultaneously connect the instrument to anotherthermocouple.

The amplifier 2 is connected to the line by suitable leads which areshown at 62, and may be disconnected from the line by a double poleswitch 63. There is also disclosed a chart driving motor 64 which may bea rotating field motor of the same type as the motor 5. This motor alsohas two of its fields connected directly to the leads 62 and the othertwo connected to these leads by a switch 65. With this arrangement thechart motor 64 may be deenergized while the potentiometer system isstill energized, but the motor is always stopped when the potentiometeris deenergized.

All of the instrument mechanism, including the parts which have beendescribed above are located within a casing 66 that may be a casting orsheet metal as desired. This casin has provisions on it whereby it canbe mounted in an instrument panel or it may be mounted against a wall.Such provisions are old in the art, and their details are not pertinentto the present disclosure. The casing is provided with a door 6'! (Fig.3) which is hinged at 68 to its right-hand side. This door is providedwith a knob 59 that serves to control a latch (not shown) and may havein it a look so that the instrument may be closed against unauthorizedtampering. The door has a window it in it through which a chart, a scaleand an indicating pointer may be seen.

Located within the casing are various of the parts which have beendescribed. For example. in Figure 6 there is shown a view of the casing66 with the potentiometer mechanism removed. It will be seen that theamplifier 2, having the vibrator 3 and the transformer 4, is mounted inthe casing on the right-hand side against the rear wall. The battery 9is mounted against the back wall as is the standard cell 52. Suitableterminal blocks for the various connections within the instrument itselfand to the thermocouples are also mounted on the back wall of thecasing.

A swinging frame 12 is hinged at H to the left-hand side of the casing.This frame is mounted so that it can be swung completel out of thecasing but may be locked into position in the casing by means of a latch'13 of the type shown in Williams Patent 2,283,304. issued May 19, 1942,which cooperates with a latch plate 74 attached to the right-hand sideof the casing. This latch is actuated by a knob 15. The frame carries onit supporting members for all of the resistors that have been describedabove, as well as the chart, the printing mechanism, the detectingmechanism and the switches for the chart driving motor and the currentsupply to the amplifier. The frame '12, as shown in Figure 3, is formedwith a pair of mechanism supporting ends and a connecting part, thatalso has various parts mounted upon it. For convenience in the followingdescription, the left end of frame [2 in Figure 3 will be referred to as12A while the right end will be referred to as HR. The connecting partwill continue to be referred to by the numeral 12.

On the upper front part of the frame 72 is a small sheet metal casing 16that extends across the width of the instrument. This casing has in itsupports 11 for various of the resistors as best shown in Figure 2. Eachof these supports is attached to a plate 18 that may be bodily removedalong with the resistors if it is desired to change the range of theinstrument. In such case all of the resistors are removed as a unit, anda new set of resistors is placed in the casing. Also mounted in thecasing 16 on the lefthand end thereof (Figure 3) is the cold junctionresistor I4 that is placed in a separate box I 4A (Figure 7) along withthe cold junctions 38 and 35. The sheet metal casing 16 is pivoted at 19on the frame portions 12A and 12B so that it may be swung up forinspection and cleaning of the slide wire 16 and collector 18 which areattached to the bottom thereof. The casing is maintained in its normalposition by a spring plunger 83 which is mounted in the frame 12A andcooperates with a small indentation on the left face of the casing. Theright-hand end of the casing receives a threaded shaft 8| having amilled head SEA which has a conical face on it. When the casing is inoperative position the shaft 8| lies, as shown in Figure 5A, in a groove32 in the frame portion 72B.

Attached to the bottom of the casing i5 is .a plate member 83 made ofsome insulating material to which are fastened the slide wire [8 and thecollector 58. These parts, as best shown in Figure 3, are not mounted onthe member 83 so that they are parallel to its sides, but are mounted ata slight diagonal. This is done so that as the contact 29 moves alongthe slide wire and collector there will be a slight wiping action whichwill tend to clean the slide wire and at the same time will cause thecontact to wear evenly rather than form a groove in its surface.

In originally calibrating the instrument it is desirable to be able toshift the slide wire relative to the contact carried by the print wheelcarriage in order to adjust the zero of the instrument. To this end theinsulating plate 83 is so mounted that it can be shifted e W Se re ativeto the bottom of the casing 16. For this purpose the casing is providedwith a tongue 84 that is punched upwardly from its bottom plate 85 asbest shown in Figure 5. A screw 86 is rotatably mounted on the tongue 84and has below the tongue 2, disk 81 to which is attached an eccentricpin 88. This pin extends into a groove 89 that is cut into theinsulating plate 83 and extends across the latter. In order to adjustthe plate which carries the slide wire relative to the casing 15, thescrew 85 is rotated to move the pin 88. As the pin, which bears in thegroove 89, is shifted lengthwise, the slide wire assembly will be movedrelative to the casing '15. The entire slide wire assembly and thecasing 16 are rigidly fastened in place on the frame 123 by the means ofthe screw 8!. When for example. the casing 16 has been lifted upwardlyaround its pivots T9 for some purpose. such as cleaning the slide wire,it may be returned exactly to its original position by means of thescrew 8!. The conical head of the screw 8i cooperates with' the groove82 in the frame to pull the entire assembly tightly against the frame12B to locate the same in some given position.

In order to shift the contact 20 along the slide wire IE to rebalancethe potentiometer in response to an unbalance thereof produced by achange in temperature of one of the thermocouples, the contact 20 isheld in engagement with the slidewir and the collector bar and ismounted on a print wheel carriage 90. This print wheel carriage hasextending from its upper rear face a clamp plate 9| in which the ends ofthe cable 80 are clamped. Therefore, as the motor 5 rotates, the printwh'eel carriage will be moved back and forth across the instrument andcarry the contact 20 with it across the slide Wire to a position ofbalance. This print wheel carriage has on it a print wheel 92 that isprovided with printing characters or numerals 93 which are to be movedinto engagement with the chart when the print wheel carriage reaches abalanced position. The manner in which the print wheel carriag operateswill now be described.

Refer now to Figures 19 to 23 which show the print wheel carriag indetail. The print wheel carriage 90 is supported at its front end by aroller 94 that is received in a channel member 95 which runs the lengthof the instrument, and is attached at its ends to the frame members 12Aand 12B. The rear end of the print wheel carriage is supported by meansof rollers 96, 91, and 98 which bear against and roll on a shaft 99 thatis also attached to the frame parts 12A and 123 at its ends. The rollers96 and are rigidly mounted on the print wheel carriage, and the roller98 is supported on a spring I00 which is attached to the print wheelcarriage. In this manner, the roller 98 is forced into engagement withthe rod 99 to prevent any upward movement be tween the print wheelcarriage and the shaft, and to keep the print wheel carriage rigidlymounted in position as it moves back and forth across the chart 2 I9.upon which the recording of the temperature is to be made. The printWheel carriage 90 has formed on one sid thereof, a downwardly extendingplate IOI which has a stud shaft I02 rigidly mounted therein. Pivoted onthis shaft is a supporting plate member I03 that has a roller I04journaled on its rear end. This roller rides in a channel member I05that is moved in a manner to be described later, for the purpose ofproducing the printing operation, and for the purpose of actuating aswitch to connect the instrument to different thermocouples.

As more particularly shown in Figure 21, the shaft I02 has a sleeve I06rotatably mounted on it. This sleeve, along with a second sleeve I08,that is rotatable on the first, is held in position on the shaft I02 bymeans of a suitable lock washer I01. The plate I03 is staked to thesleeve I08 so that the plate and sleeve can oscillate around the shaft.The sleeve I08 has a gear I09 and a ratchet wheel I I0 staked to it.Theratche't wheel serves the purpose of rotating the sleeve I08 on thesleeve I06 to rotate the print wheel and an ink pad assembly which ismounted on th former sleeve. The ink pad assembly is made of a tubularmoulding II I that may be of plastic or metal and which is formed with aseries of radially extending fin's IIIA that serve to divide thismoulding into a series of compartments. The axial bore of the mouldinghas a circular flange with a sloping face or surface H2, formed on itsright-hand side, which engages with'a cooperating surface H3 on a flangemember '4 that is suitably fastened to the sleeve I08. This member isprovided with a pin I I5 that cooperates with a groove I I6 formed in acentral opening III in the flange of the moulding III. The centralopening II'I of the flange is eccentric in shape as shown best in Figure22. The ink pad assembly is held on sleeve I00 by means of a knob I I8that has a cam face I I9 engaging the left end of the moulding and whichserves to properly center the assembly. Located within the radiallyextending compartments of the moulding i I are felt pads I20, each ofwhich may be impregnated with a different color ink if desired, so thateach of the records made of the different thermocouple temperatures willbe recorded in a distinctiv-e color. The felt pads are held in place inthe moulding by means of a shield I2I as best shown in Figure 21.

The ink pad assemby is mounted on the pen carriage by moving themoulding III containing the pads onthe sleeve I08 from the left inFigure 21. Since the printing characters 93 normally engage the ink padsI20 some means must be provided for keeping these parts separated whilthe ink pads ar being moved into place. This is the reason why thecentral opening I I! is made eccentric in shape. In mounting themoulding on the sleeve I08, the moulding is first rotated until itsgroove I I6 is lined up with pin I I5, and moved toward the right inFigure 21. The moulding is then moved clockwise from the axial positionin Figure'22 around pin I I5 as a center (counter-clockwise in Figur19') to separate the felts I20 and the printing characters 03.Thereafter the moulding is again moved to the right in Figure 21 untilits surface II2 engages surface II3. Knob H8 is then screwed into place;engagement between its surface H9 forcing surfaces H2 and H3 intoengagement with each other. Thus the moulding is rotated back into anaxial position and centered by the concentric surfaces II 3 and HQ withthe ink pads in engagement with the printing characters on the printWheel.

Also mounted on the plate I03 is a stud shaft I22. This shaft hasrotating upon it, a sleeve I 23 that is held in place by means of awasher E24. Staked to the sleeve is a drive gear I25. Also mounted onthe sleeve I23 is the print wheel 92 that is held in proper positionrelative to the sleeve by means of engagement between a slot in theprint wheel, and a pin I26 extending from the sleeve. Before the printwheel is placed on the sleeve, an indicating disc I2! is moved intoplace as shown best in Figure 23. This disc has a series of numbers onit which correspond to the print characters 93 on the print Wheel, andare so displaced with respect to these characters, that when a printingcharacter is in engagement with the chart, the corresponding numeral onthis disc will be in a position where it can be seen from the front ofthe instrument as shown best in Figure 2. A pointer I28 is attached tothe plate I03, and cooperates with the disc I21 to indicate the propernumber. The print wheel and the indicating disc are held in place on thesleeve I 23 by means of a knob I229 that is screwed on the outer end ofthe sleeve. As best shown in Figure 20, the gear I09 serves to drive thegear I25 by means of idler pinions I30, both of which are mounted forrotation on the plate I03.

Since it is imperative that the print wheel be exactly located withrespect to the print wheel carriage a spring -I3I is placed between theplate IOI of the print wheel carriage and the oscillating plate I03.This spring serves to take up any slack in the parts, and always keepsthe plate I03 properly placed, with respect to the plate IOI.

11 For a similar reason, a spring I32 is inserted between the plate I03and the gear I in order that the print wheel will be properly located onits shaft I22.

The print wheel carriage 80 is also provided on its front end, with anindictaing pointer I34 that cooperates with a scale I35, which isattached to the channel member 95 and extends across the front of theinstrument. This indicator serves the purpose of showing the value ofthe temperature being measured as it is moved in front of the scale I35.

The print wheel and the ink pads are normally kept from rotating ontheir shafts by means of a pawl I36 that is pivoted at I31 on the plateI03, and which is biased into engagement with teeth on the ratchet wheelII8 by means of a Spring I38. A roller I39 which extends from the pawlI36 engages a surface I40 on a second pawl I4! that is pivoted at I42 onthe plate IIII. This pawl MI is normally biased in a counter-clockwisedirection in Figure 20, by means of a spring I43 that is equal instrength to the spring I38. This latter pawl is used to rotate the printwheel to bring a new printing character into printing position above thechart each time a new thermocouple is connected to the instrument. Theoperation takes place due to an oscillation of plate I03 which isimparted thereto by means of the channel member I05. This channel memberis moved in an arc concentric with the stud shaft I02, by means of amechanism to be described, after the instrument has reached a balancedposition.

Cable 60 which is used for driving the print wheel carriage passes overfour pulleys I45, I45, I47, and I48, and over the drive pulley 59 thatis operated by the shaft of motor 5. This drive pulley will be describedmore in detail below. Pulley I45 is rotatably mounted on a stud I 49which projects upwardly from the arm I 50. The arm I50 is pivoted at vI5I and is biased by a spring I52 in a direction to take up all slack inthe cable. The pulley I46 is rotatably mounted on a stud I53 which iscarried by a boss that is formed in the frame I2, as best shown inFigure 8. The pulley I41 is rotatably mounted on a stud I54 which ismounted at its upper end in the frame 12 located at a point to the rightof pulley 59 in Figure 8.

The pulley I48 over which the cable 60 also passes is attached to abushing MBA that is journaled in a bearing I48B which is fastened to theframe 12A, as best shown in Figure 12A, The bearing is provided with asleeve I480 which receives the bushing. As has been previously statedthe instrument is provided with a detecting mechanism which operates todetect when the instrument comes into balance, and in response to suchbalanced position to operate a printing mechanism and connect theinstrument to another thermocouple. It will be remembered that adetecting plate 6| is moved by the cable 60 to give an indication whenthe cable has stopped moving and the printing carriage is properlypositioned. This is done by frictionally mounting the plate 6I on thebushing I48A. To this end the plate 6| is frictionally received betweena flange I56 formed as part of the bushing 8A and a washer I51 which isrotatable with the bushing but may move axially thereof. Extendingthrough the bushing is a bolt I which has between its head and thewasher .I5'I a second washer I55A. The latter washer is drawn intoengagement with the former by a spring I58 that is compressed betweenthe upper end of bushing MBA and a nut I553 The amount of frictionbetween the plate BI and the parts I56 and I5! may be adjusted byvarying the tension of the spring I58. A second nut is placed on the endof bolt I55 beyond nut I55B to lock the latter in place.

As the plate 6| is rotated along with the pulley I48 when the instrumentis in its unbalanced condition, this plate is periodically brought backto a neutral position by a cam I59 which is driven at a constant speedby the motor 64, and which cam is mounted to rotate with its drivinggear I590 on a hollow shaft I59D that is attached to and eXtends fromthe side of frame 12A (see Figure 18). The cam I59 is a three lobe camand it has three high points I60 which periodically pass through aV-shaped groove I6I that is formed in the plate 6I. One side of thisgroove is extended to form a tongue I62 on the end of the plate 6|. Thecam I59 is provided with three pawls I63 which are pivoted at I64. Thesepawls can move between the position shown in Figures 12 and 13, and thedotted line position of Figure 13 and are held in either position byengagement between the following end of the pawl and a spring I65 whichis mounted on the cam. The movement of the pawls is limited by a pin I93on each pawl which extends through an opening I94 in the cam. Each pawlis formed with a single projection I66 midway between its edges on itsleading end, and with two projections I6! adjacent the edges of the pawlon its following end. The terms leading and following refer to thedirection of travel of the pawl with the cam I59, the latter rotating ina clockwise direction in Figure 12.

In the operation of the instrument, the cam I 59 is rotated at aconstant speed. Assuming that the instrument is in an unbalancedposition and that the print wheel carriage is being moved in onedirection or the other, this means that the plate 6| will be rotated sothat the edges of the slot will bear against one side or the other ofthe cam. This plate is periodically brought into a neutral position as apoint I60 of the cam passes through the apex of the slot I6I. If theinstrument is still unbalanced, the plate 6| will have been moved eitherclockwise or counterclockwise in Figure 18, so that the tongue I52 willbe out of the path of the projection I66 and will be in the path of oneof the projections I61 by the time the pawl reaches the tongue. Thiswill continue until such time as the instrument reaches balance, whenthe plate 6| will remain in its neutral position after it has been movedthere by the cam. The tongue I52 will then be in the path of theprojection I66 on the next pawl I63 which moves past this tongue.Consequently the tongue will then engage the projection I66 and move thepawl clockwise in Figures 12 and 13 to the dotted line position of thelatter figure.

When the pawl is moved in its clockwise direction a cut-out portion I68of the pawl will be moved radially inward of the cam until it is in thepath of a pin I69 that projects from one arm of the crank I10 attachedto a shaft III journalled in the hollow shaft around I59D which the camI59 rotates. Normally durlng the time that the instrument is unbalanced,the inner surface of the pawls are at a radially greater distance fromthe shaft I'II than the pin I69, but when the instrument reachesbalance, the next pawl passing the plate BI is flipped so that its 13lower end moves inwardly to bring it into engagement with the pin I69.The crank I10 is thereupon rotated to perform the operation of printingand connecting the instrument to another thermocouple.

The outer end of the crank is provided with a roller I12 that moves in aslot I13 which is formed in the end of a lever I14. This lever isprovided with a bushing I89 that rotates on a shaft I15 whichis attachedto and extends from the frame 12A. A second lever I16 is rotatable onthe bushing I89, and has its outer end fastened to the channel member Ito move the latter. It might be noted at this point that the other endof the channel I 05 may well be fastened to a second lever, not shown,of the same length as lever I16 which second lever is pivoted at a pointcoaxial with the shaft I15 and on the frame 12B sothat the two leversand the channel I05 will form a yoke that will move as a rigid member.The lever I16 is moved by the lever I14 to actuate the print mechanismby means of a spring I19. which has one end attached to each lever. Theangular position between the two leversmay be adjusted by means of anadjustment screw I11.which is fastened to an inwardly bent tongue I 90on the lever I14 and engages an abutment I18 on the lever I16.

The crank I16 is shown in Figure 12 at its rest position. When one ofthe pawls is flipped to a driving position and the crank is rotated, thefirst action of the latter is to move the levers I14 and, I16 in aclockwise direction as the crank moves past point I80 in the cam slot.This movement serves to bring a printing character on the print wheel 92into engagement with a chart passing over the chart drum I44. If theprinting character engages the chart before the roller I12 has reachedthe point I 80 of the cam slot the spring I19 will give to permitovertravel of the lever I14. Continued rotation of the crank will firstmove the lever I14.and the parts connected to it in, a counter-clockwisedirection and then in a clockwise direction until such time as theroller I12 again reaches the position shown in Figure 12.

As the crank Irotates, it will be subjected to varying loads dependingon whether it is moving the lever I14 in one direction or the other. Inorder to smooth out the load on this crank, the shaft I1I is providedwith a disc I9I (Figure 17) to which'a cam I8I is adjustably attached bymeans of screws I92. This cam is engaged by a roller I82 that is mountedon the end of a lever I83. The lever I83 is pivoted at I84 and is biasedto bring the roller I82 into engagement with the surface of the cam by afairly stiif spring I85. As shown in Figure 17, the cam and roller arein relative positions that will be assumed when the crank I10 is at restas shown in Figure 12. It will be noticed that the roller I82 is restingin a low spot I86 on the surface of the cam to definitely locate thecrank I 10 with respect to the cam slot I13. As the crank starts torotate, cam I8I will be rotated about half-way to the high point I 81 asroller I12 reaches point I86 of the slot I13. Thereafter, the camsurface continues to rise during the time that the lever I14 is beingmoved in a counter-clockwise direction. Such operation serves to put aload on spring I85 to retard the action of crank I10 and prevent it fromrunning ahead of its driving pawl. When the crank has reached such arotative position that it starts to move lever I14 clockwise in Figure12, the cam I8I hasreached a position where its radius begins todecrease so that the force of spring I gives a slight camming action tothe shaft I1I tohelp bring the crank I10 smoothly to its rest position.

By the time crank I10 has completed itsrevolution the instrument willhave been connected to another thermocouple and will have begun torebalance itself. If the instrument has not come to balance again thetongue I62 will engage one of the projections I61 of the driving pawl tomove that pawl counter-clockwise on its pivot I64 and shift portion I68radially outward beyond the pin I69. Crank I 10 will then remain at restuntil such time as the tongue I62 is centered and engages the projectionI66 on another pawl, If, however, the instrument has rebalanced itselfprior to the time crank I10 completes a revolution the tongue I62 willbe centered and the driving pawl will not be moved out of drivingengagement with pin I69, As a result the crank will continue itsrotation and immediately proceed with another printing operation.

It is noted that a stop I88 is provided beneath the part 6! to back upthis part, and prevent its being bent, if for some reason the cam shouldexert an unduly large force downwardly on this part.

The three lobe cam disclosed in Figure 12 makes an instrument that ispractically instantaneous in printing after the instrument has come tobalance. In some cases it may be desirable to have a slightly longerdelay between the time that the instrument comes to balance and aprinting operation takes place. In such a case a two-lobe cam as shownin Figure 15 at I59A or a single lobe cam as shown in Figure 16 at I59Bmay be used. It is also noted that the speed of rotation of the cam I59may be changed to accomplish the samepurpose. By designing theinstrument with a cam with the proper number of lobes and the properspeed of rotation, almost any speed of operation can be obtained.Generally speaking, however, the speed of rotation of the cam iscorrelated with the speed and operating characteristics of the balancingmotor 5.

It may be that the print wheel carriage has practically moved intoprinting position and can be moved the remainder of the distance betweenthe time one of the points I60 of the cam I59 has centered member 6| andthe time that projection I66 of the next pawl passes the tongue I62. Ifthis is the case the tongue I62 will have moved slightly out of neutral,but not far enough to be in the path of a projection I61. A printingoperation will therefore occur. It is possible for the instrument to bealmost balanced, but not quite close enough for the above operation totake place. If this is the case tongue I62 may first engage projectionI66 and then projection I61 to first throw the pawl into and then out ofdriving position before its out out portion I68 has traveled far enoughto engage pin I69. Moving the pawls forwardly or backwardon the cam I59relative to points I60, and varying the distance between projections I61as well as the width of tongue I62 will have an effect on the amount ofmovement of the print wheel carriage that will be permitted after themember 6| has been moved to its neutral position. As an example, if thecam I59 is rotating at a speed of one revolution every three seconds,printing operations can occur at a minimum-of once every three seconds.If a three lobe cam is used a printing operation will take place withina maximum time of one second after the instrument has balanced out andmay occur in a shorter time if the instrument is almost balanced whenthe member 8I is moved to its neutral position. The maximum time thatwill occur between any two printing operations is equal to the time ittakes the print wheel carriage to move from its old to its new positionplus one second. This time, therefore depends upon the speed of motor'5.

By using various combinations of cam speeds and pen carriage speedsalmost any desired speed of operation of the recording mechanism may beobtained as shown by the table below. In the table the cam speed is inseconds per revolution; the carriage speed is in seconds for the printwheel carriage to move from one end to the other of its path of travel;and of chart is the percent of full scale travel which can be covered bythe print wheel carriage during the minimum time between two consecutiverecording operations. For example, if a two lobe cam is used and isrotating at a speed of 6 seconds and the carriage has a speed of 11seconds for full scale, a printin operation will occur every six secondsif the consecutive records are not more than 43% of the chart widthapart. If the records are further than 43% of chart width apart,printing can occur after any three seconds after the instrument comes tobalance. Again, if a three lobe cam having a speed of three seconds perrevolution is used in an instrument having a carriage speed of 22seconds, a printing operation will occur every three seconds if theconsecutive records are not more than 7.5% of the chart width apart. Ifthe records are further apart than 7.5% of chart the printing can occurwithin one second after the print wheel carriage is properly positioned.

Cam Cam Carriage Percent of Lobe Speed Speed Chart 1 3 ll 17 l 6 ll 43 1l 1 l 100 l 3 22 7. 5 l 6 22 17 1 l5 2 50 2 3 ll 17 2 6 ll 43 2 ll 100 23 22 7. 5 2 G 22 17 2 15 22 5O 3 3 ll 17 3 6 ll 43 3 15 ll 100 3 3 22 7.5 3 6 22 17 3 15 22 50 l 3 44 3. 5 l 6 44 7. 5 l 15 44 25 3 l 4 17 3 l/2 5% 17 l 44 l 60 88 50 In the operation of the print wheel, as thechannel I05 is moved upwardly, the member I03 will be moved in acounter-clockwise direction in Figure 19 or a clockwise direction inFigure 20 to bring a printing character 93 into engagement with a chartthat is placed over a chart driving drum I42.

Due to the shape of the slot I73 in lever I74 the print wheel will bemoved slowly into engagement with the chart with sufiioient force toproduce pressure printing, rather than hammer printing as is so oftenthe case in multiple recording instruments. Pressing the printingcharacter into engagement with the chart rather than dropping it intoengagement therewith produces quieter operation as well as being easieron the various parts. When the print character engages the chart thespring I79 will flex to permit lever I14 to move through its fullstroke. Upon continued rotation of shaft I'II the lever I14, as has beendescribed, will be moved downwardly in Figure 12. This means that themember I03 will be moved counter-clockwise in Figure 20 with the pawlI36 in engagement with ratchet H0 thus preventing any relative rotationof the parts mounted on member I03. As this movement continues theroller I39 on pawl I36 will move to the right along the surface I40until such time as the lever arm between roller I39 and the pivot I42for pawl I4I has been shortened enough fOr the force of spring I43 toovercome that or spring I38. At that time the pawl I4I will move intoengagement with the ratchet I I0 and, acting through the arm I40, willmove pawl I36 out of engagement with the ratchet. This will occur at thebottom of the stroke of lever I74, and with the printing wheel in itshighest position above the chart drum. Continued rotation of the crankI70 will then begin to move the lever I14 clockwise in Figure 12, whichmeans that member I03 will move clockwise in Figure 20. During thismovement the pawl MI is in engagement with the ratchet I10 and willthereby prevent that ratchet and the gear I09 from rotating relative tothe part IOI. While the member I03 is moved clockwise, however, idlersI30 and gear I25 upon which the print wheel is mounted will rotate,thereby moving the print wheel clockwise in Figure 20 andcounter-clockwise in Figure 19 to bring a new printing character intoprinting position above the chart drum. As this clockwise movement ofthe part I03 continues the roller I39 will move away from the pivotpoint I42 and the lever arm between I39 and I42 will become large enoughfor spring I38 to overcome the force of spring I43. At this time thepawl I36 will move into engagement with the ratchet I I0 and maintainthe parts in the position shown until the next printing operationoccurs. It will be seen, therefore, that the ratchet is positivelylocked for movement with the part I03 by pawl I36 or is positivelylocked against movement by the pawl I4I. At no time is the ratchetwheel, and therefore the print wheel, free to rotate because the pawlsare so designed that pawl MI is moved into engagement with a tooth ofthe ratchet as pawl I36 is moving out of engagement therewith. It will,therefore, be seen that as the crank I70 starts to rotate after theinstrument has come into balance its movement will produce a printingoperation and then an operation whereby a new printing character isbrought into printing position above the chart.

The same movement of the channel member I that brings the print wheelinto engagement with the chart and rotates the print wheel also servesto connect another thermocouple to the instrument. This is done byrotating brushes in a switch into engagement with other contacts of theswitch. A switch by means of which this may be accomplished is shown atI55 (Figure 8) in the drawings and may well be of the type described andclaimed in Harrison Patent 1,770,918, issued April 22, 1930. Such aswitch is provided with a shaft I95 by means of which the brushes may berotated. As shown herein, the switch is mounted on a bracket I91 that isattached to a portion of the frame 12A.

I of a ratchet 205.

The movement of the channel member I acts to'rotate the shaft I96 bymeans of a connector I98 (see Figure 17) which is attached to thechannel member near one end and which is pivoted to one end of afloating link I99, the other end of which is pivoted to one arm of alever 200. This latter lever is mounted for rotation around a shaft 20Iand has mounted on its other arm a pawl 202 that is pivoted at 203 onthe lever. Pawl 202 is biased by means of a spring 204 in a directionwhich will bring its end into engagement with one or the other of theteeth Movement of the lever 220 is used to rotate the ratchet and abevel gear 206 that is attached thereto, both of them being mounted onthe shaft 20I. The pawl 202 is provided with a roller 201 that isadapted to move along a surface 208 formed on one arm of another pawl209 that is pivoted at 2G0 on a plate 2II. This plate forms part of abracket 2I2 that serves to support the switch actuating mechanism andthe shaft 20I. Pawl 209 is biased in a counterclockwise direction byspring 2I3 which i equal in strength to the spring 224. Beveled gear 209meshes with a beveled pinion 2I4 that is attached to the upper end of ashaft 2I5 which serves to rotate the switch shaft I96. Shafts 2I5 andI96 are joined together by means of a universal joint which, in thiscase, comprises a spring metal plate 2I6 that is fastened to the shaft2I5 at diametrically opposed points 2!! and is fastened to the shaft I96at point 2I8. The universal joint serves to compensate for any slightmisalignment that may appear between shaft 2 I 5 and I96.

On the initial upward movement of the channel member I95 when a printingope-ration takes place, the pawl 202 will move the ratchet 295 a slightamount in a clockwise direction. This movement is imparted theretothrough link I99 and lever 200, and has no effect on the switch exceptto move its brushes slightly backwards on the contacts. When, however,the channel member I05 starts its downward movement in Figure 17, thelever 200 is moved in a counter-clockwise direction and acts through thepawl 202 to rotate the ratchet 205 also in a counter-clockwise direction. This movement i imparted to the gearing and through shaft 255 toswitch 95 to connect another thermocouple into the potentiometercircuit, the arrangement being such that the connection is madeimmediately after the downward movement begins. It will be seen thatimmediately after the printing operation takes place the switch isadjusted to connect another thermocouple to the instrument. After thisoperation is performed, the upward movement of the channel I05 is usedto reset the pawl and ratchet mechanism of the pen carriage, and theswitch adjusting mechanism. While this adjusting movement is takingplace, the potentiometer is being rebalanced so that no unnecessary timeis lost between printin operations. The ratchet mechanism used foradjusting the switch is similar in operation to that previouslydescribed which was used on the print wheel carriage. As the lever 200moves counter-clockwise, roller 20! will move toward the pivot 2I0 untilsuch time as the leverage between the two pawls changes enough for theforce of spring Elli to overcome that of spring 20 4. When this occurs,pawl 202 will be lifted out of engagement with the ratchet, and pawl 209will move into engagement with the same. This occurs near the bottom ofthe stroke of lever 200. Thereafter, as lever 200 moves in a clockwisedirection, the ratchet wheel 18 will be held from turning by pawl 209 aspawl 202 is moved to a position in which it can engage the next tooth onthe ratchet wheel.

The chart, which has been mentioned above, is shown best at 2I9 inFigure 2. It will be seen that the chart is provided with horizontal andvertical lines, and has on one edge a series of round holes 220, and onits opposite edge a series of slots 22!. The horizontal lines on thechart serve the purpose of indicating the time at which some particularrecord is made, while the vertical lines or calibration marks serve toindicate the value of the temperature that has been recorded. As bestseen in Figure 12, the supply roll 222 of the chart is mounted betweenthe frame portions 12A and 1213 near the bottom, and toward the rear ofthe frame. The chart, when being inserted into the instrument is pulledupwardly, and forwardly over the rod 223. The chart is then threadedtoward the rear of the instrument between a guide member 224, and thechart drum I49. This guide member serves to .irect the chart around thedrum, from which it is brought down across the front of the instrument,and over a chart backing plate 225 to a chart take up roll 226, which islocated at the bottom of the frame directly in front of the sup-plyroll.

The backing plate 225 is preferably hinged at its lower end, as shown at221, so that it may be moved out of the way when a new chart is to beinserted into the instrument. The backing plate is held in place bymeans of a pair of lock members 228 that engage cut-out portions 229 onthe upper corners of the backing plate.

These locking members are held in engagement with the portions 229 ofthe backing plate by means of spring members 230 upon which they aremounted.

The supply roll 222 and the take-up roll 220 are mounted at their leftends in Figure 2, or their right ends in Figure 8 in the frame portion12A, upon a spring mounted chuck 23I shown in Figure 10 which is adaptedto be wedged into the end of the core 232 of a supply or take-up roll.Thi chuck is attached to a shaft 233 that is mounted for rotation in abushing 234 inserted in the frame 12A. The chuck is forced to the leftin Figure 10 into engagement with the end of the roll by means of aspring 235, and is limited in its movement bya washer 236 on the outerend of the shaft. It will be noted that the shaft 233 is made of a largediameter near the chuck and a small diameter to the right thereof. Thisconstruction gives a large and rigid bearing surface near the end of thechart roll and permits the use of a bushing 234 of the type shown whichfully encloses the spring 235.

The left end of the supply roll 222 in Figure 8 or the end in frameportion 123 is mounted on e. non-rotatable chuck 292, shown in Figure11, that is attached to a shaft 293 which is threaded through the frame12B. This shaft may be provided with a knob 294 to rotate it and shiftthe chuck axially. In any event a lock nut 295 is threaded over theshaft and is jammed against the frame to hold the chuck firmly inposition when it has been adjusted. Since the chuck 292 is non-rotatableit serves to put a drag on the supply roll to prevent the same fromover-running. Both the chuck which supports the left end of the supplyroll and that which supports the left end of the take-up roll, to bedescribed below, are axially adjustable so that the rolls may be shiftedto the proper position relative to the chart drum 144. The right end ofthe take-up roll 226 adjacent frame portion 123 is supported by anadjustable and rotatable chuck 231 shown in detail in Figure 8. Thechuck is provided with a tongue 238 that is adapted to engage the usualdriving notch formed in the end of the roll core (see Figure 2). Thistongue extends through an opening in the edge of the chuck and is formedof spring material which always acts to move out into the positionshown. When inserting a roll over a chuck of this type, the tongue 238will be moved against the flange of the chuck. Thereafter, as the rollor the chuck is rotated, the tongue will spring into its drivingposition as soon as the driving notch of the core is in alignmenttherewith. The chuck 231 is attached to a shaft 239 whose outer end isprovided with a knob 249 whereby the chuck can be rotated at will tosupply or take up slack in the chart. The shaft 239 is journaled in asleeve 241 that is threaded through an opening in the frame 1213. Theouter end of this sleeve is provided with a thumb nut 242 whereby thesleeve can be rotated in order to shift the chuck to its proper axialposition and is provided with a lock nut 243 that can be jammed againstthe side of the frame to hold the sleeve in place.

The chuck used for the take-up ro'-l has attached to the shaft 239 asprocket 244. This sprocket is driven by a chain 245 that extends over asecond and larger sprocket 246. An idler sprocket may be used againstthe chain to take up slack if this is deemed necessary. In order tocompensate for increasing diameter of the chart on the take-up drum thesprocket 246 is frictionally driven by the chart drum 144 by means of a.pair of friction washers 241 that are keyed to a shaft 248 on the end ofthe chart drum. The sprocket and the friction washers are moved togetherand against a nut 249 that is screwed on the shaft by means of a plate259 which is forced to the left bv springs 252. Each of the springs 252surrounds a plunger 25! which is attached to the plate 259 and which isfreely movable through openings that are formed in the end of the chartdrum. In order to adjust the tension of the springs. and therefore thefriction with which the sprocket 246 is driven, the nut 249 may be movedto the left or right along the shaft 248.

The chart drum in this embodiment of the invention is driven at aconstant speed by the motor 64 through a. gear train 253 that startswith the pinion 54A (Figures 12 and 18) and ends with the gear 254 thatis frictionallv mounted on the drum. It will be seen from Figure 2 thatthe chart drum is provided on each end with a series of projections 255that project through the openings 220 and 221 in the chart. By means ofthese projections and openings the chart is positively moved past theprint wheel at some given speed. The speed of the chart drum may ofcourse be changed by substituting a different gear reduction between themotor and the chart drum. The shaft 248 upon which the chart drum ismounted is provided with a knob 256 by means of which the chart drum maybe rotated to properly position the chart with respect to the printwheel. There is also provided amember 296 which extends over the edge ofthe chart and which can be used as a guide to properly set the timelines on the chart relative to the print wheel and a so-called tear-ofistrip 251 which is made of some transparent material and which extendsacross the shaft by a set-screw 299.

the instrument in front of the chart. The purpose of this member is toact as a straight edge when a piece of th chart is to be removed.

The drive motor 5 which serves to move the print wheel carriage back andforth across the chart is mounted beneath the chart and behind thebroken portion of the frame as shown in dotted lines in Figure 8 and inFigure 9. This motor has extending therefrom a shaft upon which ismounted a pinion 258 that meshes with and drives the gear 58 to which isattached the pulley 59 around which cable 60 is wrapped. The gear 58 ismade with teeth around most of its peri hery and is provided with aprojection 259 either sid of which can jam against the pinion to limitrotation of the gear and therefore travel of the print wheel carriage.Gear 58 and pulley 59 are attached by rivets or other suitable means toa sleeve 26B that is rotatable on a shaft which is suitably attached toand projects from the rear of frame 12. Roller bearings 291 are providedbetween the sleeve 266 and shaft EM, and the sleeve is held on the shaftby a bolt 298 which is prevented from rotating relative to If it isdesired the cable 60 may be attached to the pulley 59 by any suitablemeans to prevent the possibility of any slippage occurring between thetwo.

The instrument is also disclosed as being provided with a switch S,shown in Figure 8, that can be used to actuate a signal when somepredetermined temperature occurs, or for any desired control purpose.The switch S herein is operated by a cam 262 that is mounted on thesleeve 26B, and held in proper position thereon by spacer members 396and a thumb nut 361. The cam has a cut out portion 263 that is joinedwith the surface of the cam by inclined edges 264 and 265. The switchitself is mounted on a plate 256 that is suitably attached to the frame12. Attached to the plate 266 and insulated therefrom is a piece ofmaterial 261 upon which the switch blades are mounted. One blade isshown at 258, and has a contact 269 on its right end. The second bladeis numbered 219 and is shown as being pivoted to the member 261 at 21!.This blade has a contact 212 on its right end which is adapted to engagewith the contact 269 and is normally held in engagement with thiscontact by means of a spring 213. Also mounted for rotation around point21! is a lever 214 which has a roller 215 projecting from it intoengagement with the surface of the cam 262.

In the operation of the instrument, it may be assumed that the gear 53and cam 262 are rotating in a clockwise direction in Figure 8. From theposition shown in that figure, the rotation of the cam 262 will move thecut-out portion 263 to the right, and cause roller 2'55 to ride upinclined surface 264 to an idling position on the surface of cam 262with the contacts 263 and 212 closed. Thereafter upon a reverse movementof the earn 262, or a movement in a counter-clockwise direction, theroller 2% will bear on the e: ge of cam 262 until first the inclinedsurface 294 and then the cut-out portion 263 comes under the roller, atwhich time it will return to the position shown in the drawing.Continued rotation o the cam will move the roller 215 up the surfaceagain to the edge of the cam. As this is taking place, th left side oflever 2T4 will move into engagement with the left end of switch. blade270. and thereby move that blade around its pivot and against the forceof spring 273 to separate the switch contacts. Continued rotation of thecam

